Ubiquitous surface protein A2 (UspA2) is a trimeric autotransporter that appears as a lollipop-shared structure in electron micrographs (Hoiczyk et al. EMBO J. 19: 5989-5999 (2000)). It is composed of a N-terminal head, followed by a stalk which ends by an amphipathic helix and a C-terminal membrane domain. (Hoiczyk et al. EMBO J. 19: 5989-5999 (2000)). UspA2 contains a very well conserved domain (Aebi et al., Infection & Immunity 65(11) 4367-4377 (1997)), which is recognized by a monoclonal antibody that was shown protective upon passive transfer in a mouse Moraxella catarrhalis challenge model (Helminnen et al. J Infect Dis. 170(4): 867-72 (1994)).
UspA2 has been shown to interact with host structures and extracellular matrix proteins like fibronectin (Tan et al., J Infect Dis. 192(6): 1029-38 (2005)) and laminin (Tan et al., J Infect Dis. 194(4): 493-7 (2006)), suggesting it can play a role at an early stage of Moraxella catarrhalis infection.
UspA2 also seems to be involved in the ability of Moraxella catarrhalis to resist the bactericidal activity of normal human serum. (Attia A S et al. Infect Immun 73(4): 2400-2410 (2005)). It (i) binds the complement inhibitor C4bp, enabling Moraxella catarrhalis to inhibit the classical complement system, (ii) prevents activation of the alternative complement pathway by absorbing C3 from serum and (iii) interferes with the terminal stages of the complement system, the Membrane Attack Complex (MAC), by binding the complement regulator protein vitronectin. (de Vries et al., Microbiol Mol Biol Rev. 73(3): 389-406 (2009)).
Moraxella catarrhalis is an important and common respiratory pathogen that has been associated with increased risk of exacerbations in chronic obstructive pulmonary disease (COPD) in adults. (Sateesh et al., Journal of Chronic Obstructive Pulmonary Disease 3:109-115 (2006)).
A need for vaccines for Moraxella catarrhalis exists.